1. Field of the Invention
Aspects of the present invention relate to a flicker reducing and/or preventing apparatus of a fluorescent lamp, and more particularly, to an apparatus to reduce and/or prevent flicker of a fluorescent lamp that occurs when a switch is turned on and/or off.
2. Description of the Related Art
An image forming apparatus, such as a printer, a multi-function printer, and others include a CCD module to scan an image. Such a CCD module includes a fluorescent lamp for illumination.
For the effective driving of the fluorescent lamp, a direct current (DC) of 24 V is supplied to the fluorescent lamp when electric power is initially supplied to warm up the fluorescent lamp, a DC of 18 V is supplied to the fluorescent lamp during the scanning thereof, and a DC of 12 V is supplied to the fluorescent lamp during a standby state.
A pulse width modulation (PWM) control is utilized to adjust the voltage that is to be supplied to the fluorescent lamp in accordance with the driving statuses of the fluorescent lamp, as listed above.
As shown in FIG. 1A, an activated PWM control signal PWM_LAMP of “LOW” state is applied to a transistor Q1 of a first switching unit A2 via an inverter In to turn on the transistor Q1 so that a field effect transistor (hereinafter, referred to as an ‘FET’) Q2 is turned on and a DC voltage (such as 24 V) is supplied to the fluorescent lamp L. Accordingly, a PWM control signal PWM_LAMP corresponding to a magnitude of the voltage supplied to the fluorescent lamp is outputted and time when the transistors Q1 and Q2 are turned on is varied so that the DC voltage supplied to the fluorescent lamp L via a smoothing unit A1 can be adjusted. Reference numerals R1, R2, and R3 indicate resistors, a reference numeral C1 indicates a capacitor to remove noise, and a reference numeral Be indicates a bead inductor to remove noise.
As shown in FIG. 1B, when a power switch S/W provided in the image forming apparatus is turned on, a power supplying unit 1 converts an alternating current (AC) voltage into a plurality of direct current (DC) voltages such as DC of 24 V and DC of 5 V, and supplies the converted DC voltages to a controller 2. DC of 24 V is supplied to drive the fluorescent lamp L, and DC of 5 V is supplied to drive the various respective components of the image forming apparatus.
As shown in FIG. 1C, any one of the DC voltages, such as DC of 5 V that is supplied by the power supplying unit 1, is stabilized after a transient period T1 elapses, and the other of the DC voltages, such as DC of 24 V is stabilized after another transient period T1+T2 elapses.
After the transient period T1+T2 elapses, a reset signal output from a reset generating circuit (not shown) is stabilized, and the initializing of the respective components (not shown) is performed by the stabilized reset signal.
After the stabilization of the reset signal, the stabilized DC voltage of 24 V is supplied to the fluorescent lamp L so that the fluorescent lamp L is warmed up.
According to a related art technique to supply voltage by way of PWM control, as shown in FIGS. 1A-1C, when the power switch S/W of the image forming apparatus is turned on, the controller 2 of the image forming apparatus must output the activated PWM control signal to warm up the fluorescent lamp L after the reset signal is generated to reset the various components of the image forming apparatus. However, although the power switch S/W is turned on, if the DC voltage that is output from the power supplying unit 1 of the image forming apparatus does not reach a stabilized state (such as DC of 5 V), but yet the controller 2 outputs the activated PWM control signal PWM_LAMP such as DC of 3 V (during a transient period T1 when the power ramps up), the fluorescent lamp L may flicker when the DC voltage is supplied to the fluorescent lamp L. Moreover, when the fluorescent lamp L is turned off by having the power switch also turned off, the fluorescent lamp L may flicker because the controller may output the activated PWM control signal PWM_LAMP.
As such, when the unexpected flicker of the fluorescent lamp occurs, a flash of bright light is instantaneously emitted from the fluorescent lamp and the flash may surprise a user in spite of a cover over the fluorescent lamp. Moreover, since an inrush current may be introduced instantaneously into the fluorescent lamp when the fluorescent lamp is turned on for a short time, the current becomes a factor in shortening the lifespan of the fluorescent lamp.